We previously demonstrated that AKT1 is the true human counterpart of v-akt and recently detected frequent elevated AKT1 kinase activity in primary tumors of prostate, breast and ovary. We have also observed that activated AKT1 transforms NIH 313 cells and induces membrane ruffling and that DN-AKT1 inhibits ras transformation. In addition, two AKI 1 -interation proteins have been identified, one of which is APciB that contains 4 AKT 1 phosphorylation sites and 3 SH3 domains, and the other is a proteasome b-subunit (PMSB4) that has an AKT1 phosphotylation site. AKT1 phosphorylates APaB and PSMB4 in vitro and in vivo. Moreover, APaB binds to PAK 1 kinase and enhances AKT1-induced cell survival and cell growth. We have also shown that AKI I phosphorylates p21 WAFI and abrogates p21 inhibitory effect on CDK4/6 and cdc2 kinases. Activated AKT1 overrides p5 3-induced Gi arrest. Based on these data, we hypothesize that that activated AKT1 and its associated proteins are cross-talk with PAK1 and p21 WAFi pathways to contribute to the control of malignant transformation, cell cycle progression and cytoskeleton reorganization. Thus, AKT1 could be a valuable tumor marker and a critical target for therapeutic intervention in human cancer. The broad, long-term objective of this project is to elucidate the normal cellular function of the AKT1 protein and determine the importance of perturbations of AKT1 pathway in human cancers. The specific aims are: 1. Determine the clinicopathologic significance and the role of AKT1 activation in prostate and breast cancer. This will be accomplished by (a) examining AKT1 activation in a large series of primary prostate and breast carcinomas and correlating AKT1 activation with clinicopathologic features, and (b) creating prostate-specific, probasin promoter-driven AKTJ transgenic mice to ascertain if overexpression of activated AKT1 is tumorigenic. 2. Define the interaction between AKT1 and two potentially important signaling partners identified by the yeast two-hybrid system. We will examine (a) the effects of AKT 1-interaction proteins on AKT1 cell survival pathway, including PAK1 activation, Bad phosphorylation, NFiB activation, cytochrome c release, cytoskeleton reorganization, and p27 degradation, (b) the effects of AKT 1-interaction proteins on AKT1 oncogenic activity, and (c) the importance of the binding domains between AKT1 and its associated proteins in AKT1 signaling. 3. Examine the effects of AKT1 phosphorylation of p21 on cell cycle control. This will be accomplished by examining the effects of AKT1-induced p21 phosphorylation on (a) subcellular localization of p21 and p21 binding ability to cyclinlCDK complexes, (b) cyclinlCDK activity, (c) assembly of Gi cyclinlCDK complexes and PCNA binding activity, and (d) p21-induced cell cycle arrest. 4. Determine AKT1 as a critical target for cancer intervention. This will be accomplished by examining (a) the effects of direct inhibition of AKT1 on cancer cell growth, (b) the effects of DN-AKT1 and activated AKT1 on sensitivity of chemotherapeutic drugs, and (c) potential AKT1 inhibitors' specificity and ability to inhibit tumor cell growth in vitro and in vivo.